1. Field of the Invention
The present invention relates to a liquid nebulizing (atomizing) technique, and more particularly, to a nozzle plate of a spray apparatus and its manufacturing method.
2. Description of Related Art
Liquid nebulizing systems have become more widely adopted in various applications such as drug delivery systems in the biomedical field, atomizing fuel for internal combustion engines in the automotive field as well as the heat radiation using liquid exchange in the HVAC field. All of the foregoing applications employ nebulization theory and examples of relevant patents include U.S. Pat. Nos. 4,465,234, 4,605,167, 6,089,698, 6,235,177 and 6,629,646, Taiwanese Patent Numbers 407529, 449486, 503129, 506855 and 562704, as well as the Taiwanese Patent Cert. Number 1222899.
Most of the conventional designs for the nozzle plate of the spray apparatus employ a piezoelectric actuator as a vibrator with a matched nozzle plate 20 having a plurality of orifices 201 as illustrated in FIGS. 8A and 8B, thereby allowing a nozzle plate 20 to come into immediate contact with a liquid 21 to be nebulized. Electrical voltage is applied to the piezoelectric actuator to vibrate liquid 21 in a holding reservoir and spray the liquid 21, such that the liquid 21 departs from the nozzle plate 20 through these orifices 201, thereby creating a fine mist. However, in that the design of the conventional nozzle plate 20 is a geometric structure with mirror symmetry, the liquid 21 in the device is ejected in a direction perpendicular to the exterior surface of the nozzle plate 20 (as shown in FIG. 8B) such that coverage of mist ejection is subject to position and size of the orifices 201 of the nozzle plate 20, thus resulting in a narrow nebulizing range that leads to accumulation of the nebulized droplets due to collisions. This not only increases the size of the nebulized droplets but also diminishes the nebulizing effect. Also, if the coverage of nebulization is to be increased, the number of orifices or the driving frequency of the piezoelectric actuator must be increased, or both, thereby increasing system volume, not to mention that a large driving area requires a higher resonance mode. As a consequence, both liquid and energy consumption will be increased.
U.S. Pat. No. 4,465,234 discloses an application of a semi-circular nozzle plate on a spray apparatus that changes the geometric shape of the nozzle plate so as to increase the nebulizing area. The nozzle plate of the spray apparatus includes a nozzle plate having a cavity for containing a liquid, a nozzle installed on the nozzle plate and communicating with the cavity, a piezoelectrically actuated vibrator installed on the nozzle plate and configured to pressurize the liquid cyclically, filling means for filling and maintaining the liquid in the cavity, electric means for supplying an alternating voltage to the piezoelectric actuator to drive vibration, and means operatively coupled with the filling means for delivering the liquid. When the liquid in the cavity is pressurized, the liquid is sprayed in the form of a mist, and, because the design adopts a nozzle plate having an arc-shaped nozzle, the mist range increases.
U.S. Pat. No. 4,605,167 proposes an ultrasonic application of a nozzle plate of a spray apparatus. Such an application of the nozzle plate of the spray apparatus increases the mist range by expanding the spraying range of the orifices. Even though such a conventional technique increases the mist range, the larger spraying range of the orifices requires a higher operating frequency for the piezoelectric actuator, and, therefore, the energy consumed by driving the spray apparatus is also increased, leading to the disadvantage of excessive spray apparatus volume, which poses a problem of accumulation of the nebulized droplets.
U.S. Pat. No. 6,089,698 proposes a method and a device for forming a nozzle. The method comprises directing a high-energy laser beam towards a face of a nozzle plate so as to form a nozzle bore in the nozzle plate, thereby controlling the ejecting direction for the expelled droplets. Also, Japan Patent Number 2002-115627 proposes a two-step process for forming orifices on the nozzle plate surface, thereby controlling the ejection direction of the liquid droplets. However, the laser process is a technique that is unable to easily control the droplet propagation direction and the Japanese method is complicated, and thus the problems of a narrow nebulization range as well as ineffective nebulization are still not solved.
U.S. Pat. No. 6,235,177 discloses an application for manufacturing a nozzle plate of a spray apparatus. By forming aperture orifices on the top and bottom surfaces, the liquid droplets are ejected at a high speed along the axes of the orifices. In the U.S. Pat. No. 7,040,016, the orifices formed by the etching process are symmetrical with respect to the axis. However, the aforementioned conventional technique creates a symmetrical design for the orifices employed by the nozzle plate of the spray apparatus, but employing such a technique will limit perpendicular propagation of the liquid droplets, and the mist area is still limited by the position of the orifice openings as well as the size of the openings. As such, disadvantages in the above-mentioned patents still exist involving ineffective nebulization.
Based on the above explanations, the conventional liquid nebulization techniques cause the problems of nebulization failure, limitation of the nebulizing area by the opening size, droplet accumulation due to spraying by concentrated orifices, over-sized spray apparatus, and complicated manufacturing processes for the nozzle plate, thereby leading to ineffective nebulization, a waste of resources, difficulties in product miniaturization and disadvantages in manufacture.
Hence, it has become an urgent issue to designers of the nozzle plate of the spray apparatus to propose a technique that overcomes the foregoing difficulties.